Multiple-electrode discharge tube and method of manufacturing same

ABSTRACT

A multiple-electrode discharge tube comprises a plurality of disc electrodes arranged one above another and fused with the envelope therefor. Each of the odd-numbered electrodes has a reduced diameter and a reduced thickness as compared with the even-numbered electrodes. Fusion takes place by way of high frequency heating coils disposed around the electrodes of reduced thickness. This provides a uniform heating of all of the electrodes for fusion, and avoids partial overheating of the envelope.

Ll. Uite States atent 1 [111 3,872,343.

Furuta 1 1 Mar. 18, 1975 [54] MULTIPLE-ELECTRODE DISCHARGE 2,409,855 10/1946 Hillyer, Jr. et al 313/300 X 2,740,067 3/1956 Sorg 313/250 X 2,808,528 10/1957 Martin 313/250 X 2,899,590 8/1959 Sorg ct a1 313/257 X Inventor: Shigeru Furuta, Tokyo, Japan Kabushiki Kaisha Sankosha, Tokyo, Japan Filed: Apr. 13, 1973 Appl. No.: 351,170

Related U.S. Application Data Division of Ser. No. 211,917, Dec. 2-7, 1971, Pat. No. 3,771,205.

Assignee:

US. Cl 313/296, 313/250, 313/257, 313/306 Int. Cl. H0l'j 1/46, 1-l0lj 21/10 Field of Search 315/250, 257, 296-300; 313/306, 307, 250, 257, 296-300 References Cited UNITED STATES PATENTS 4/1942 Roman 313/250 X Primary Examiner-Alfred E. Smith Assistant ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or FirmWenderoth, Lind & Ponack [57] ABSTRACT A multiple-electrode discharge tube comprises a plurality of disc electrodes arranged one above another and fused with the envelope therefor. Each of the oddnumbered electrodes has a reduced diameter and a reduced thickness as compared with the even-numbered electrodes. Fusion takes place by way of high frequency heating coils disposed around the electrodes of reduced thickness. This provides a uniform heating of all of the electrodes for fusion, and avoids partial overheating of the envelope.

2 Claims, 5 Drawing Figures PATENTEU MAR] 75 FIG! FEG. 2

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EATING TIME FIG.4

mmDP/EMQE MULTIPLE-ELECTRODE DISCHARGE TUBE AND METHOD OF MANUFACTURING SAME This is a division of application Ser. No. 211,917, filed Dec. 27, 1971, now US. Pat. No. 3,771,205.

BACKGROUND OF THE INVENTION The invention relates to a multiple-electrode discharge tube of the layer-built type, and in particular, to such discharge tube having more than two electrodes in which an intermediate electrode is a disc electrode having a diameter greater than either the upper or lower electrode. The invention also relates to a method of manufacturing such discharge tube. 2

Prior art multiple-electrode discharge tubes of the kind described have been fabricated by fusing the electrodes to the envelope of the tube with high frequency heating, and both top and bottom electrodes as well as the intermediate electrode were of a common thickness. In these prior art methods, a high frequency coil is disposed around the envelope and energized to produce magnetic flux which intersects each of the electrodes to thereby generate heat for fusing purposes. However, in view of the higher flux density around the intermediate electrode compared to the relatively low density around the upper or lower electrode, and because of the greater diameter of the intermediate electrode, more flux is intersected by the intermediate electrode. As a result, a difference in temperature occurs between this intermediate electrode and the upper or lower electrode, which results in the envelope softening initially around the intermediate electrode and then after a short time delay around the upper and lower electrodes. The delay-results in the overheating of the glass envelope so that it is hotter than is required for fusing with the electrodes. This causes strains to be produced in the glass envelope with consequent poor quality of the product.

The division of the high frequency coil into two parts disposed to surround the upper and lower electrodes, respectively, still fails to prevent premature heating and fusing of the intermediate electrode by virtue of the increased flux density around the intermediate electrode which results from the sum of the fields created by the respective coil parts.

OBJECT OF THE INVENTION Therefore, it is an object of the present invention to provide an improved multiple-electrode discharge tube which overcomes the above difficulty.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, it will be described below with reference to the drawings in which:

FIG. 1 is a schematic elevational section of a prior art triode discharge tube of the layer-built type arranged with a high frequency heating coil,

FIG. 2 is a similar view of the discharge tube constructed according to the invention,

FIG. 3 is an elevation, partly in section, of the discharge tube shown in FIG. 2,

FIG. 4 shows graphically the relation between the fusing temperature and heating time for various electrode thicknesses and FIG. 5 is an elevational section of the discharge tube constructed according to the invention, using disc electrodes to constitute a pentode structure.

Referring to the drawings, FIG. 1 shows a prior art discharge tube which includes an upper electrode 1, a lower electrode 2 and an intermediate electrode 4, all of which have an equal thickness. These electrodes are fused with an envelope 3, which may comprise glass, by means of high frequency heating coil 7. Asmentioned previously, more flux is intersected by the intermediate electrode as compared with the upper or lower electrode, with the consequence that the temperature of the intermediate electrode rises more rapidly than the latter and hence is supplied with an additional amount of heat until the time when the other electrodes become sufficiently heated to permit their being fused with the envelope 3.Such overheating of the intermediate electrode causes strains in the glass envelope and degrades the quality of the product.

Referring to FIGS. 2 and 3 which show one embodiment of the invention, the intermediate electrode indicated at 4A has an increased thickness as will be noted from a comparison with the electrodes 1 and 2. The in termediate electrode 4A has a discharge electrode 5 and an aperture 6 formed therein which provides an ion path for inducing a discharge across the electrodes 1 and 2 from the initially occurring discharge across the electrode 4A and the electrodes 1 and 2. In FIG. 2, reference numerals 8 and 9 represent divided parts of a high frequency heating coil disposed only around the thinner electrodes 1 and 2, respectively. The assembly is enclosed in a bell jar 10.

Referring to FIG. 4 which shows the relation between the fusing temperature and the heating time, the curve designated A represents the diagram for the thin electrodes 1 and 2, curve Bfor a thin intermediate electrode 4, and curve C for a thick intermediate electrode 4A. The points at which fusing takes place are indicated at 17 and 18 on the respective curves.

FIG. 5 illustrates another embodiment of the invention and shows a discharge tube having five electrodes.

The top electrode '1 is thin, the second electrode 11 from the top is thick, the third electrode 12 is thin, the fourth electrode 13 is thick, and the bottom electrode 2 is thin. In other words, odd-numbered electrodes are thinner and smaller in diameter than even-numbered electrodes, while even-numbered electrodes are thicker and greater in diameter. High frequency heating coils 14, 15 and 16 are disposed only around thin electrodes 1, 12 and 2.

From the foregoing description, it will be appreciated that the problem associated with the manufacturing of a discharge tube as illustrated in FIG. 1 is solved in accordance with the invention by replacing the ordinary intermediate electrode 4 by a thicker one as shown at 4A in FIG. 2. While more flux from the high frequency heating coil is intersected by the the thick intermediate electrode 4A than by upper or lower electrode 1 or ,2,

the increased heat capacity of this intermediate electrode due to its increased thickness causes a shift in the time for reaching the fusing temperature to the point 18 of FIG. 4. By contrast, where all of the electrodes are of a common thickness as illustrated in FIG. 1, the intermediate electrode will reach the fusing temperature at the point 17 (curve B) of FIG. 4, while the upper and lower electrodes reach the same temperature at the point 18 curve A) of FIG. 4, thereby producing a time delay t. The invention eliminates this delay, and permits the intermediate electrode 4A to be sealingly fused concurrently with the upper and lower electrodes, thereby achieving the favorable result of an improved product.

It has been found that when the thick intermediate electrode 4A is used, dividing the high frequency heating coil into two parts disposed only around the upper and lower electrodes 1 and 2 also avoids the time delay and permits concurrent fusing of all of the electrodes, even though the flux density may be increased around the intermediate electrode as compared with the other electrodes. It has also been found that such division of the high frequency heating coil is effective for a multiple-electrode discharge tube where there is an intermediate electrode of similar diameter and thickness as the top and bottom electrodes, as illustrated at 12 in FIG. 5.

While the envelope of the discharge tube has been described as comprising glass, it should be obvious that it may comprise ceramic material. Where a ceramic envelope is employed, the electrode is provided with a melting metal for fusion with the envelope. For this arrangement, the invention is again effective to prevent undesired flow and attachment of the melting metal to other functional surfaces which might occur if the electrodes involve differential time periods to reach a melting temperature, and which would degrade their mechanical strength and other functions.

Thus, there has been described an extremely simple and effective means for manufacturing, with good yield, a multiple-electrode discharge tube of the layerbuilt type in which an intermediate disc electrode positioned between upper and lower disc electrodes has a greater diameter than the latter.

Having described the invention, what is claimed is:

1. A multiple electrode discharge tube comprising:

a cylindrical glass envelope having a substantially uniform outer diameter;

at least one first disc-shaped electrode member positioned to extend through said envelope at a position intermediate the opposite ends of said envelope;

a plurality of second disc-shaped electrode members positioned to extend through said envelope at positions on opposite sides of said at least one first electrode member; 7

each of said at least one first electrode members having a thickness and a diameter greater than the thickness and diameter of each of said plurality of second electrode members;

the outer edges of each of said first and second electrode members extending externally of the outer surface of said envelope and forming connecting terminals; and

said envelope being fused and rigidly secured to said electrode members at the portions thereof extending through said envelope. v

2. A tube as claimed in claim 1, wherein said envelope has opposite open ends, the two outermost of said second electrode members sealingly closing said opposite ends. 

1. A multiple electrode discharge tube comprising: a cylindrical glass envelope having a substantially uniform outer diameter; at least one first disc-shaped electrode member positioned to extend through said envelope at a position intermediate the opposite ends of said envelope; a plurality of second disc-shaped electrode members positioned to extend through said envelope at positions on opposite sides of said at least one first electrode member; each of said at least one first electrode members having a thickness and a diameter greater than the thickness and diameter of each of said plurality of second electrode members; the outer edges of each of said first and second electrode members extending externally of the outer surface of said envelope and forming connecting terminals; and said envelope being fused and rigidly secured to said electrode members at the portions thereof extending through said envelope.
 2. A tube as claimed in claim 1, wherein said envelope has opposite open ends, the two outermost of said second electrode members sealingly closing said opposite ends. 